BPHORSEGUY

I have a brand new 383 Stroker Motor built by one of the top Manufacturers and bought thru Summit. It was installed by the most reputable Corvette shop in my Area. I have not talked to anybody about this yet mostly due to Memorial day weekend. I have not driven the car much only about 300 miles! Just added the 3rd quart!!! I did notice smoke at highway speeds when letting off. I went for a club ride today and 3 or 4 of my friends said the car was smoking most noticeably from the right side when letting off the gas. I have done 3 or 4 short rides and about 120 miles today! The car has been parked in the same place all the time and the ground is completely dry under the car! I cannot get the car to have a reliable idle under 1000 rpm and sometimes it will act loaded up and drop to 500 rpm or less, I attributed this to being new but now think I may be getting intermittent fouling. The car runs liked a raped ape except for the idling issues and now the smoke. The smoke was noticeable from the cockpit at the highway part of the drive home from the shop WHEN LETTING OFF THE GAS but is not noticeable now from the rear view mirror! My plan is to drive the car some more this weekend and contact the installer on Tuesday. What do the experts say!

BPHORSEGUY

Post was duplicated dont know why?

BPHORSEGUY

Post duplicated when I tried to edit but the point I was trying to edit is that the smoke is when I let off the gas especially at higher speeds!

zmanabba

I would suspect a leak at the intake manifold gasket at the lower part of the port. This would allow oil to be sucked in to the intake port and there would be a vacuum leak causing the high idle

BPHORSEGUY

The high idle is caused by me, I can't get a reliable consistent idle below 1000 rpm!

kossuth

New build.... Could be alot of things. Could be blow by from either improperly installed rings etc. Hope that's not it. If you have a PCV setup / breather back into the air cleaner it's possible your valve cover baffling isn't sufficient to keep oil from being drawn into the motor. Or possibly your crankcase ventilation is just jacked and it's drawing oil in through the breather because the PCV valve or breather isn't doing it's thing properly. Could be a vacuum leak on the lower side of one of the intake manifold gaskets and it's sucking oil in from the lifter valley.

If you have a PCV system on the car stick your finger over the breather part for about 10-15 seconds with the engine running at idle. If you feel a vacuum that parts good. If you don't feel a vacuum pull the hose off the PCV itself and make sure you have a vacuum from the carb/intake manifold. The valve should rattle if you shake it.

A lower intake gasket would be tough find particularly if you have a PCV plumbed in on the car. You would see alot of crank case vacuum on a gauge if that gasket is no good. If you look down inside the intake manifold do you see oil?

zmanabba

This is also a symptom of a vacuum leak. I wouldn't do too much since you should have a warranty but you might consider at least seeing if the bolts from the intake to the heads are torqued correctly

kossuth

Very possible....

GTR1999

I had an oil usage issue with the 350 I built for my 72. I checked all the usual things- pvc, intake gaskets, did leak down and compression test, all checked out but I was using a qt of oil in about 600 miles. It would foul the plugs in no time. Just short of pulling the engine I spoke with Lars and he told me to check the valve seals. The heads were World SR Torquers and they were originally equipped with umbrella seals, that were shredded. To make the swap fast I had the original heads rebuilt and cut for positive seals. Make the swap and solved the problem, the positive seals worked. No oil usage in between 3k mile changes.

jackson

Intake gasket
Valve stem seals
Ring(s)

ClothSeats

I agree with valve seals. The symptoms you described (smoke during idle and when letting off the gas) are high vacuum conditions, which cause the vacuum to pull oil past the valve seal into the combustion chamber. You will know which cylinder is the cuprit before long because that spark plug will be fouled so bad it will quit firing.

derekderek

letting off gas is high vacuum. rings will blow oil under load. smoke at high vacuum is a valve guide problem or intake manifold leak. idle problem points to vacuum leak. so manifold gasket most likely culprit. cheapest and easiest too. i generally put silicon under manifold gasket. set gasket in place, using the china wall gaskets as they have gasket locators built into them. set the manifold with no sealer above gasket on and walk away. come back in an hour or so and lift manifold off. now you get to see exactly where gasket is and is going to stay. remove china wall gaskets and replace with a bead of silicon.

Jebbysan

Put a vacuum gauge on it......is the needle steady or does it bounce? If it does, you have a leak in the induction side.
Pull the plugs, are they dark and starting to get build up on them? 150 miles a quart would foul plugs pretty quickly.
has this engine been dyno'd and broke in? Rings break in under heavy load or WOT blasts......if the rings are not broke in, you will get a lot of oil going past them.....and a lot of blow by. Is there excessive crankcase pressure?
Valve seals also can be a culprit as stated.....check the other two things first then pop the covers off for inspection......

Jebby

Rescue Rogers

I think its the valve seals, I had that same issue and then noticed I didnt have any valve seals.

jackson

One issue or another for some Six Weeks.
Unless YOU blew the Intake install, seems ATK screwed the pooch.

BPHORSEGUY

Can't disagree with you but this all could be one problem !. First thank you all for helping! Earlier posts suggest PCV. I am no expert but if it was wouldn't it smoke evenly, it is 90% right side. It does not excessively smoke during WOT so can I rule out rings? Definetly smokes during high vacuum situations as several have stated!

jackson

Evenly,No not necessarily

There are two discrete gaskets; one for each bank of V8's cylinders.

One side-gasket can seal 100% while gasket on other bank leaks.

No, you cannot rule out rings unless-until correct orientation is verified eyes-on.

BPHORSEGUY

So... short story, this is it!

jackson

Suggest pull carb off and inspect plenum for oil AND pull all sp plugs and note position and inspect for oil-fouling.

BPHORSEGUY

That sounds like a logical start!